The present invention relates to a radio frequency aperture which may be placed in a RF beam for the purpose of steering the RF beam, focusing the rf beam and/or changing its polarization.
The present invention relates to an antenna aperture and to the material to be used in an antenna aperture. This disclosed material is capable of performing various functions on a Radio Frequency (RF) beam passing through it by behaving as a tunable dielectric. The material includes a plurality of layers, each layer containing an array of small electrically conductive, preferably metallic, plates disposed therein. The plates in each layer preferably overlap with those of the neighboring layers, thereby forming capacitors. The lateral dimensions of the individual plates preferably measure much less than one wavelength of the frequency or frequencies of interest for the RF beam so that the material can be considered as an effective dielectric medium, with the conductive plates behaving as lumped capacitive circuit elements as opposed to behaving as radiating elements of an antenna.
Since each layer includes an array of plates and since the material includes a plurality of layers, a three-dimensional array of capacitors is provided which enhances the effective dielectric constant of the material. The dielectric effect is nonisotropic and depends on the density and arrangement of capacitors, so the dielectric tensor can be and preferably is, a function of location in the material. By moving, preferably by translational movements, each layer relative to its neighboring layers, the value of each capacitor, and thus the effective dielectric tensor, can be changed. In this manner, an arbitrary dielectric function can be obtained, and this dielectric function can be reprogrammed with only a small amount of movement of individual layers in a three dimensional array formed by a stack of layers.
This material can be effectively used as an antenna aperture where it can behave as a quasi-optical element. Having a programmable dielectric tensor allows it to perform a variety of operations in an antenna aperture. For example, it can be configured as a radio frequency tens or prism, to focus or steer a radio frequency beam, or as a quarter-wave plate, to convert a radio frequency beam between circular and linear polarization. Applications for such a material include tracking of one or more satellites and sending or receiving two polarizations of radio signals simultaneously from a single antenna installation.
The present invention also provides a method of steering an RF beam over a wide angle with only a small mechanical movement being required, if any is needed at all. Prior art approaches for RF beam steering generally involve using phase shifters or mechanical gimbals. With this invention, beam steering is accomplished by variable capacitors, thus eliminating expensive phase shifters and unreliable, bulky mechanical gimbals. The variable capacitors can be tuned with a relatively small differential mechanical motion, or alternatively, they can be tuned by electronic actuation. Furthermore, using this approach if the layers in the material are differentially moved in two orthogonal directions, then only two orthogonal controls are required to scan in two dimensions, eliminating the complexity of controlling many radiating elements independently. This invention does not depend on a particular feed method, and can be placed over an existing prior art antenna aperture of a dish antenna in order to add the functionality of beam steering to such a device. Furthermore, it can be used with receiving and/or transmitting antennas.
This invention also provides a method for converting between linear and circular polarization, which is important for satellite communications. It also allows two signals with opposite circular polarization to be steered independently, thus allowing the possibility of tracking two satellites simultaneously. In the prior art, this would be accomplished using two separate antennas.
The present invention allows a RF beam in the microwave frequencies, for example, to be manipulated in much the same way that visible light is manipulated by optical lens"" and/or by quarter wave plates.
Generally speaking the present invention provides a radio frequency aperture comprising a plurality of insulating layers disposed in a stack, each layer including an array of conductive regions, the conductive regions being spaced from adjacent conductive regions.
In another aspect the present invention provides method of bending or steering radio frequency waves impinging an on antenna. The method includes disposing a plurality of insulating layers arranged in a stack between a source of the radio frequency waves and the antenna, wherein each insulating layer includes an array of conductive regions, the conductive regions being spaced from adjacent conductive regions and forming capacitive elements; Also the capacitance of the capacitive elements in the plurality of insulating layers is adjusted as a function of their location in the plurality of insulating layers.